AoI-Constrained Transmission Scheduling with HARQ and Heterogeneous Sampling Processes.

We consider a hybrid automatic repeat request (HARQ) based status update system where timely information from multiple sources with different sampling processes (uncontrollable and controllable sampling) is sent via a transmitter to a destination through an error-prone channel. To minimize the average number of transmissions subject to an average age of information constraint, we propose a near-optimal deterministic transmission policy. We formulate a constrained Markov decision process (CMDP) problem and provide a solution using the Lagrangian relaxation method and relative value iteration algorithm. Numerical results show that the proposed policy achieves near-optimal performance.